In the normal course of railroad track maintenance it becomes necessary from time to time to remove existing ballast from beneath the ties and replace it with fresh ballast. This is often done without disturbing the rails and ties of the track itself. Apparatus for conducting this type of operation is well known in the art and one general type of machine comprises a track travelling vehicle having a vertical rotary trench digging wheel at one side of the track and a horizontally disposed undercutter for removing the ballast from beneath the ties of the track. Examples of this type of machine are seen in U.S. Pat. Nos. 4,563,826 issued Jan. 14, 1986 and in 4,674,208 issued June 23, 1987. This type of machine relies on the indirect approach of delivering the ballast from the undercutter to a conveyor, or to the trench, from which it is removed by the digging wheel. Also, the machines are generally large and because of the necessity to separate the track undercutter longitudinally on the machine frame from the rotary trench digger, the frame of the machine requires to be quite long.
A somewhat different approach is taken in the U.S. Pat. No. 3,967,396, issued July 6, 1976, the disclosure of which is incorporated herein by reference, in which the horizontal undercutter, instead of depositing ballast in some fashion in the path of the trench digging wheel, as in the previously given examples, is actually arranged with the outer end of the undercutter within the wheel so that ballast removed by the undercutter is deposited directly into the wheel and falls into the buckets thereof. While this configuration has the advantage that the track working machine can be arranged on a much shorter length chassis, it suffers from the disadvantage that, in order to accommodate the end of the undercutter within the wheel, the wheel itself has to be of a diameter such that the trench dug thereby is quite deep.